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42 To date, more than 500 bridge structures in North America have had cathodic protection systems installed. Many of the early systems were experimental and their design, installa- tion, and operation for a certain period have been docu- mented. To obtain a good understanding of the long-term performance, a history of performance for at least half or more of its projected service life should be available. This would allow one to reasonably ascertain if the claims made with regard to extension in service life are realistic. As there are various types of cathodic protection systems, the long- term performance is dependent on the materials and compo- nents used. When reviewing the performance of cathodic protection systems, it is important to ascertain the impact of design and the installation quality on its performance. Cathodic protection systems of the same type on various different installations have provided a varied performance and sometimes performance has been limited by inadequate design, improper installation, or inadequate monitoring and maintenance. In 1995, as a continuation of SHRP, the FHWA initiated an effort (FHWA-54) to monitor for 5 years the performance of various different types of cathodic protection systems on highway structures that were operational at that time and/or were just installed. Various materials in various configura- tions had been used as anodes resulting in various different types of cathodic protection systems. The selection of the anode material and its configuration is paramount to the suc- cess of the system. The primary objective of this study was to determine the effectiveness of various materials and config- urations when used as anodes on highway structures through a long-term evaluation. In this effort, a total of 20 highway structures (19 bridges and one tunnel) protected by one or more types of cathodic protection system(s) were included. The structures were located in 11 states and 1 Canadian province. These structures were protected by a total of 19 impressed current and 5 galvanic cathodic protection sys- tems. There were 9 different types of anode materials and configurations used in impressed current and 3 different types of anode materials and configurations used in galvanic cathodic protection systems. The length of time the systems had been in operation at the end of the program varied from 1 to 15 years. The results of this effort were published in 2000 (27). The findings of this report are briefly reviewed along with the response of various public agencies to the sur- vey conducted in this effort. Where possible, information on long-term performance available in literature for systems that have moved beyond research and experimentation and have become mainstream systems is also included. IMPRESSED CURRENT CATHODIC PROTECTION SYSTEMS Slotted Non-OverlayâConductive Polymer Backfill One of the largest slotted conductive polymer non-overlay cathodic protection systems was installed on the bridge car- rying I-64 in Charleston, West Virginia, which was energized in 1985. This system was still operational at the time of this report and although the system has undergone repairs, no concrete repairs have been required since the start of opera- tion. This system was monitored under the FHWA-54 pro- gram and monitoring and maintenance appeared to be a major problem for the owners. A consultant was hired to monitor and maintain the system and it had a documented history of satisfactory operation until 2005 when it was last monitored. The anode material in a few slots experienced acid attack and the conductive polymer material had failed. The primary anode, platinum niobium wire, and the secondary anode, carbon fiber, were exposed to the traffic and were damaged. These were repaired after approximately 7 years of operation. The West Virginia system uses platinum as the primary anode in the longitudinal slots and carbon fibers in the transverse slots. This system does not have an overlay and the conductive polymer in the slots is exposed to loading from vehicular traffic. Missouri has the largest inventory of slotted cathodic pro- tection systems. Its oldest system has been in operation for 23 years. Of its 161 bridge deck systems, 38 are mixed metal oxide titanium systems, 8 have platinum and carbon wire, and the remainder of the systems uses platinum wire as the anode material. It should be noted that all slotted systems in Missouri have an overlay. Only 10 slotted bridge deck sys- tems have asphalt overlay; all others have a concrete overlay. The cathodic protection systems on the bridge decks prevent corrosion of the embedded reinforcement and its electric field also forces the chloride ions to migrate away from the reinforcement toward the positive anode material, thereby reducing the chloride ion content in the deck concrete. Recently, when the bridge decks with cathodic protection systems had to be widened, the chloride ion distributions in the decks were evaluated. When the chloride content at the CHAPTER SIX LONG-TERM CATHODIC PROTECTION SYSTEM PERFORMANCE
43 top mat steel depth was in excess of 2 pounds per cubic yard, a cathodic protection system was reapplied after widening; otherwise, a dense concrete overlay was used. In two projects for bridge widening, a total of 27 bridge decks were evalu- ated. These bridge decks had been protected by cathodic protection systems for a minimum of 10 years. A total of 10 bridge decks did not require reapplication of the cathodic protection system; on 15 bridge decks the cathodic protection was reapplied and 2 bridge decks were replaced. The experiences of Missouri clearly indicate that the application of cathodic protection not only extends the ser- vice life of the reinforced concrete structure but can revert it to a chloride contamination state, which does not require cathodic protection. No other corrosion mitigation system, with the exception of electrochemical chloride extraction, can do that. Mixed Metal Oxide Six mixed metal oxide systems were monitored under the FHWA-54 project; the mesh form of the anode was used in five and the ribbon was used in one. The mesh anodes were installed on the decks of three bridge structures. The deck systems had been operational for 6 to 12 years by the end of the evaluation and were judged to be operating satisfactorily. The ribbon anode was installed on a bridge deck and was documented to be performing well after 9 years of operation, and in the survey it was reported to be operational at the age of 16. The mesh anode has been installed on marine substruc- ture elements of several bridges in Florida and is either encapsulated in gunite or installed in a jacket system. The oldest of these is the gunite encapsulated system, which was in operation for 19 years at the time of reporting and had only minor repairs to correct failed gunite (53). The authors of the Florida report expect this type of system to provide a service life extension in the range of 50 years. The oldest operational system in Missouri was installed in 1989 and was operating sat- isfactorily after 19 years. Since 1990, Ontario has been using the mixed metal oxide mesh anodes on bridge decks with a cementitious overlay and waterproofing and has had signifi- cant success with this system. Service life is projected to be in the range of 25 to 30 years. Connecticut has 12 bridge deck systems that have been operational for 15 to 18 years. This anode material has proven to provide the longest extension in service life and has one of the highest current discharge capacities among other available materials. Arc Sprayed Zinc The second largest application of arc sprayed zinc in Oregon is on the Yaquina Bay Bridge and protects 283,300 square feet of concrete surface area. This system was energized in 1996 and was monitored under the FHWA-54 effort until 1998. The installation of the system on the arch spans was completed in 1991 and on the south approach spans in 1995. Up until 1996, the systems were operated as a galvanic cathodic protection system. At the start of the operations as an impressed current system there were issues with the remote monitoring and remote control of the system and many zones were not outputting sufficient current to meet the 100 mV shift criteria. The problems with the remote monitor- ing and control systems were worked out and the systems were outputting current density of 2.2 mA per square foot of concrete surface area (54). The oldest operational system in Oregon is on the Cape Creek Bridge, which has been opera- tional since 1989. Conductive Paint A conductive paint system had been operational on the Yaquina Bay Bridge for 17 years when reported in 2004 (54). Two conductive paint systems were monitored by the FHWA-54 project and both of them were located in Virginia. One was installed on the hammerheads of the bridge carrying I-95 over the James River in Richmond and the other was on the hammerheads of the bridge carrying I-81 over the Maury River in Lexington. Both systems provided adequate protec- tion while they were operating. The conductive paint was deteriorating owing to exposure to the elements and the sys- tem on the I-95 bridges had reached the end of its service life after 9 years of operation, and the system in Lexington was exhibiting signs of paint deterioration after 5 years of opera- tion. The systems on the bridges of I-95 were replaced and the Lexington Bridge was replaced. Although the conductive paints may have a shorter service life, especially when exposed to the elements, it is fairly inexpensive to reapply the paint and extend the remaining service life. GALVANIC CATHODIC PROTECTION SYSTEM There is a tendency for many agencies to use the galvanic cathodic protection systems because they do not need the level of monitoring and maintenance that impressed current cathodic protection systems require. These are finding appli- cation on marine substructure elements and superstructure elements exposed to deicing salts. Arc Sprayed Zinc Arc sprayed zinc is being used primarily on marine substruc- ture and superstructure elements. Research has indicated that the resistance of the system can be maintained within accept- able limits if sufficient moisture is available. Direct wetting of the zinc system is most effective in maintaining the delivery of adequate current by the system (55). This anode is suitable for application above the tidal zone. On the drier superstructure elements where direct wetting of the system is not possible, the zinc anodes suffice because corrosion rates are generally lower in these locations and the galvanic sys- tems are able to provide adequate cathodic current. In Florida
44 alone, arc sprayed zinc has been applied in 36 projects and protects 677,053 square feet of concrete surface area. The old- est such system was installed in 1989 on the Niles Channel Bridge and was operational for 17 years. Three systems were evaluated under the FHWA-54 pro- gram and all of them were installed on marine substructure elements. The experimental system on the Queen Isabella Causeway in Texas was only 1 year old at the end of the proj- ect and was performing well. The Howard Frankland Bridge in Tampa and the Seven Mile Bridge in the Florida Keys had arc sprayed zinc systems that were 5 and 7 years old, respec- tively, at the end of the evaluation. The Howard Frankland Bridge system was performing well; however, the Seven Mile Bridge was providing less than adequate protection. The Seven Mile Bridge has epoxy-coated rebar and the cathodic protection system was installed to provide protection to the epoxy-coated rebar. Over the last five years, Ontario has increasingly used arc sprayed zinc and the aluminumâzincâindium alloy as cathodic protection anodes on piers, girders, and caps and their moni- toring data indicate good performance to date. Zinc Mesh Anodes in a Jacket The zinc mesh anodes in a jacket have been used in Florida since 1994. To date, these types of galvanic cathodic protec- tion systems have been used on 51 projects and installed on approximately 1,782 piles. At least 16 structures have these systems, which have been in operation for more than 10 years. FDOT has a program to monitor and maintain them and their data to date indicate that, in general, these systems are pro- viding adequate protection. Overall Long-Term Performance Cathodic protection systems that are properly designed, installed in accordance with standard practice and good work- manship, and adequately monitored and maintained have per- formed well. The agencies that have committed to the use of this technology and have made resources available have reaped the long-term benefits and have reduced their overall maintenance costs. Several different types of cathodic protec- tion systems have been demonstrated to provide service life extension of at least 20 years, and are expected to continue to provide protection.
